The machine disclosed in Korean Patent No. 425814 issued to the inventor of this invention has a plurality of stacks to be laminated. The stacks are supported by a pair of guides so as to move up and down. A button unit having buttons corresponding to the number of stacks is formed in front of the stacks. The button is advanced by a solenoid to be inserted into the insert groove of the stack, and then retracted by a button fixing/releasing device installed in another button to return to its original position when another button is advanced. The button unit is fixed in front of a plate positioned above the stack.
In addition, as a selected one of the solenoids makes an adjacent button advanced, the selected stack is moved up or down along the guide by means of a wire when a user pulls or releases a handle, as an example.
However, such a weight-training machine inevitably requires an external power source to operate the solenoid, so it should be installed at a place where external power may be supplied.
In addition, since the button unit having solenoid and button is positioned at a front center of the stack, the center of gravity is inclined forward on the basis of a bearing of the guide when the stack moves up and down. Such an inclined load causes mechanical friction applied to the bearing, thereby deteriorating the exercising sense.
In addition, power lines of the solenoids are fluctuated up and down when the stack moves up and down, thereby giving bad appearance.
The compact weight-training machine disclosed in Korean Patent Application No. 2003-49609 filed by the inventor of this invention is configured so that a weight adjustment device has a minimum length by crossing two moving devices (a weight unit and an exercising unit) in opposite directions to each other so as to maximize the leverage effect. Thus, the machine occupies a small space, advantageously in space utilization rather than conventional ones. In addition, the machine has an advantage that a length of the wire that should be pulled by a user is not changed though a point of action is changed.
However, a motor-driven weight-training machine among such machines requires an external power source to operate the motor, thereby causing space limitation.
In addition, since a significant amount of electricity is consumed to operate the motor of the weight adjustment deice, the machine cannot use an independent power generating mode.
A conventional stack 17 has a cubical shape as shown in FIG. 20. A fixture insert hole 18a is formed in the center of the front surface toward a rear side in a certain depth. Meanwhile, a fixing rod insert hole 15a is perpendicularly formed through the center of the upper surface so as to be crossed with the fixture insert hole 18a. In both sides of the fixing rod insert hole 15a, guide holes 16a are formed to pass through vertically.
In addition, as shown in FIG. 22, a plurality of stacks are laminated on a base 11. The stacks are laminated to be capable of moving up and down along guides 16. A fixing rod 15 of a plate 14 combined to the guides 16 is inserted into the fixing rod insert hole 15a. 
In addition, as shown in FIG. 21, a fixture 18 is inserted into the fixture insert hole 18a to pass through a hole of the fixing rod 15. Thus, the corresponding stack 17 and other stacks 17 laminated thereon are used for exercising.
However, such a stack 17 has a disadvantage that the fixture 15 is not easily inserted if it is once separated for weight adjustment since the fixture insert hole 18a has a small diameter.
In addition, the fixture 18 may be separated from the stack 17 even during exercising. In this case, no load is applied to the exercising handle connected to a wire 13, thereby causing various accidents. For example, a user may fall down backward from the seat or the handle may hit the head or the face of the user, depending on the kind of the weight-training machine.
In this point of view, the inventor discloses an improvement that solves such problems in Korean Patent No. 425814.
As shown in FIG. 19, a weight adjustment device 200 having buttons 230 corresponding to the number of stacks 30 is installed at a front center of the stacks 30. The buttons 230 are moved forward or backward manually or automatically (using a solenoid) so that a fixing plate of the buttons 230 is inserted into an insert hole. Thus, it solves the conventional inconveniences that, after being released from the fixture insert hole 18a, the fixture 18 of the stack 17 should be inserted again into a fixture insert hole 18a of another stack 17, and that the fixture 18 is separated from the fixture insert hole 18a during exercising to cause accidents.
In addition, an upper end of the weight adjustment device 200 is combined in front of the plate 210, and a top of the plate 210 is fixed to the stack 20. Thus, there is no need to separately install the conventional fixing rod 15.
However, since the stack 30 has the circular insert hole at the center of the front surface and the fixing plate has a circular rod shape, the stacks 30 are eccentrically inclined in right and left directions during vertical movement. In addition, since the fixture 18 should be provided with at least an operation distance to pass the center of gravity of the stack 30 on the basis of front and rear of the stack 30, the machine requires more force in comparison to a button switch manner, namely a one-touch manipulation.
In the figures, reference numeral 10 designates a support, 12 designates a pulley, 13 and 112 designate wires, and 23 designates a wire fixture, respectively.